The prime purpose of this research will be the delineation of the role of the gallbladder in the pathogenesis of cholesterol gallstones, utilizing both acute and chronic experiments in primates (baboons and rhesus monkeys) with intact extrahepatic biliary systems. Gallbladder tone is to be determined by study of pressure/volume relationships in the gallbladder; factors altering tone, including pharmacologic and hormonal manipulations, will be evaluated. Following these studies, which will define the physiology of gallbladder motor function, the effect of gallbladder tone on both the partitioning of hepatic bile flow between gallbladder and duodenum and on gallbladder emptying will be determined. Anatomic alterations such as sphincteroplasty and vagotomy will be performed and the subsequent change in bile salt physiology monitored. Finally, effects of changes in bile composition on gallbladder motility will be studied. BIBLIOGRAPHIC REFERENCES: Robin, S. and Armstrong, M.: Biliary Lecithin Secretion. II. Effects of Dietary Choline and Biliary Lecithin Synthesis. Gastroenterology, 70:397-402, 1976. Shaffer, E. and Small, D.M.: Gallstone Disease.in Current Problems in Surgery, July, 1976.